The International Latitude Service was created by the International Geodetic Association in 1899 to study variations in latitude caused by polar motion, precession, or "wobble" of the Earth's axis.
|Alternative names||International Polar Motion Service|
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The original International Latitude Observatories were a system of six observatories located near the parallel of 39° 08' north latitude. The alignment of all six stations along the parallel helped the observatories to perform uniform data analysis. The original six observatories were located in:
Twelve groups of stars were studied in the program, each group containing six pairs of stars. Each night, each station observed two of the star groups along a preset schedule and later compared the data against the measurements taken by the sister stations. Economic difficulties and war caused the closings of some of the original stations, though a newer station was created in Uzbekistan after World War I. The data collected by the observatories over the years still has use to scientists, and has been applied to studies of polar motion, the physical properties of the Earth, climatology and satellite tracking and navigation.
The final six observatories were located, in order of Longitude (E to W), in:
The ILS was renamed International Polar Motion Service (IPMS) in 1962. It was replaced when the International Earth Rotation Service (IERS) was established in 1987.